The present invention relates to a device for transmitting torque from an internal combustion engine to a secondary assembly, in particular to a compressor of an air conditioning system of a motor vehicle.
In motor vehicles equipped with an air conditioning system, the compressor of the air conditioning system is usually driven by the crankshaft of the internal combustion engine via a belt drive. If the compressor of the air conditioning system fails, the result is that the entire drive train of the motor vehicle is blocked and the vehicle is no longer drivable. In order to remedy this deficiency, European Application (EP) 0,793,031 A1 discloses a device in which a means for vibration damping and for overload protection is arranged between the compressor belt pulley connected to the crankshaft via a belt drive and the hub of a compressor shaft. The vibration damping means is intended to ensure that when a predetermined torque, specifically the torque occurring due to the standstill of the compressor, is exceeded, the compressor shaft is uncoupled from the belt pulley, so that the belt pulley can rotate freely and the functioning of the remaining drive train is not impaired if the compressor fails. In addition to this overload protection, the known vibration damping device also provides, at the same time, vibration damping, in order to keep away from the compressor or the compressor shaft harmful vibrations which are transmitted from the crankshaft to the belt pulley via the belt drive. In this context, the known vibration means is formed by an elastic driver element which is connected fixedly to the hub of the compressor shaft and, on the outside, is connected to the belt pulley elastically in a particular way. The elasticity of this driver element is dimensioned in such a way that, when a predetermined torque occurs, this driver element slips and thus ensures overload protection.
Since this driver element serves both for vibration is damping and for overload protection, it has proved very difficult, in practice, to design this driver element exactly in such a way that it both performs the vibration damping function satisfactorily and ensures overload protection exactly when the predetermined torque occurs.
A generic device is known from German Patent Application 198 21 990 A1. In this device, the means for vibration damping and overload protection is formed by two separate components. The vibration damping means is formed by a rubber ring and the overload protection is formed by a coiled spring which is mounted on the drive shaft and is arranged and designed in such a way that it is deformed when the load arises. If the overload situation occurs, the transmission of torque from the drive shaft to the belt pulley is interrupted reversibly, as long as the overload occurs. It is difficult, however, to design such a spring exactly in such a way that it ensures the overload function reliably when the predetermined torque arises. Moreover, if the overload torque fluctuates, a virtually oscillating state may be established since the coiled spring transmits the torque or not, depending on the torque.
A similar device is known from U.S. Pat. No. 3,372,561. In this device, too, the overload protection has a spring element, thus entailing the same disadvantages.
An object of the invention therefore is to improve a generic device in such a way that both the desired vibration damping is ensured and an exactly responding and functionally reliable overload protection is ensured.
In a device of the type designated initially, this object is achieved, according to the invention, in that the component for overload protection is formed by a driver disk which is held positively on the hub in such a way that the transmission of force between the hub and the driver disk is terminated directly and permanently when a specific predetermined torque is exceeded.
According to the invention, therefore, a device is proposed, in which uncoupling of the two functions likewise takes placexe2x80x94that is to say one component is provided for vibration damping and the other for overload protection. The components can therefore be designed separately from one another, so that both satisfactory vibration damping and exactly responding overload protection in the case of a predetermined torque can be ensured. At the same time, the design of the overload protection reliably ensures that, when the overload torque arises, irreversible separation takes place between the hub and the driver disk, so that after the overload situation has arisen, further transmission of torque is ruled out. Undesirable instances of damage in the drive train when an overload torque arises on the secondary assembly can consequently be reliably avoided.
There is provision, particularly preferable, for the component for overload protection to be formed by a driver disk which is positively and/or nonpositively held fixedly in terms of rotation on the hub in such a way that the connection is broken in the case of a specific predetermined torque. In this case, the positive and/or nonpositive hold can be implemented in various ways. There being provision, particularly preferably, for the positive and/or nonpositive connection between the driver disk and the hub to be formed by a profiling resembling a splined shaft and having indented splines. In this case, the positive and/or nonpositive connection is then designed in such a way that, when a predetermined torque occurring due to the standstill of the compressor shaft is exceeded, the profiling resembling a splined shaft can slip freely, so that transmission of torque between the hub and driver disk is canceled.
The driver disk is preferably composed of plastic, while the hub consists, for example, of sintered metal. A suitable choice of the plastic and profiling then makes it possible, depending on the blocking torque caused by the standstill of the compressor to achieve an exact design such that the overload protection takes effect precisely when the compressor is at a standstill.
In a further advantageous embodiment, there is provision for the driver disk to be provided at the outer edge with drivers spaced circumferentially from one another. Each driver in each case engages into a driver space of the belt pulley. The drives space is delimited in each case by radial ribs. The component for vibration damping is formed by elastomeric elements coming to bear between the edges of the respective driver and the associated ribs of the belt pulley. The elastomeric elements may then be designed in a controlled manner such that the desired vibration damping can be implemented, irrespective of how the overload protection is designed.
The elastomeric elements may be designed in various ways may therefore be advantageously designed as a common annular part, thus making assembly particularly simple.
They may, alternatively also be vulcanized onto the respective ribs of the belt pulley or onto the respective driver.
There is provision, in a particularly advantageous way, for the elastomeric elements to have a concavely curved design at the radial ends and to be provided centrally with a central hole. Under pressure stress, the central hole is then deformed elliptically and the rubber deflected outward can be pressed into the radial concavely curved portions and therefore not undergo any friction on the belt pulley.